Luxembourg Patents LU No. 81.207 and LU No. 81.859 describe a process for refining pig iron, based on influencing the physical properties of the slags as well as the kinetics of the decarburization reactions in the converter, by a directed introduction of inert gases through the bottom of the vessel.
The treatment of molten metal and slags with inert gases makes it possible to prevent the slag from developing a foamy consistency, thus avoiding the formation of a voluminous thermally insulating layer on top of the metal bath. Furthermore the kinetics of the oxidation of the carbon contained in the bath by the top-blown oxygen become controllable.
In these systems, a layer of foam-free slag floats on the surface of the metal. By contrast with earlier, conventional processes, a much higher afterburning of CO-gases generated during the decarburizing of the bath takes place right on the surface of the bath, whereby a larger portion of the energy liberated during afterburning is transferred to the bath itself since the foam-free slag layer hinders the heat transfer less than a foam layer would.
Thanks to this increased availability of energy compared to conventional blowing processes, this method allows for scrap charges in the order of 450 kg/Ton of steel to be fed to the melt. Charges of this magnitude prohibitively cooled earlier melts.